Swimming pools have long been filtered. The filter system on a swimming pool consists of one or more inlets, a pump, and one or more outlets. As the pools are open to the environment, they are subject to contamination by a variety of items of a variety of sizes. In order to trap the larger items which may fall into the pool, including leaves, larger bugs, etc., the inlets to the pump are equipped with a device called a skimmer.
A swimming pool skimmer is essentially a cavity containing a basket. Water enters the skimmer from the pool at the side of the cavity, above the basket. Water exits the skimmer at the bottom of the cavity, below the basket. Debris from the pool follows the water into the skimmer and is trapped in the basket.